Reference is made to commonly-assigned U.S. patent application Ser. No. 09/627,802 filed concurrently herewith, entitled xe2x80x9cProcess for Laminating Electrically Addressable Displayxe2x80x9d by Dwight J. Petruchik, the disclosure of which is incorporated herein.
1. Field of the Invention
The present invention relates to electrically addressable displays and, more particularly, to a process for selectively removing a light modulating layer containing a liquid crystalline material in a polymeric binder from the electrically conductive layer of a liquid crystal display substrate.
2. Background of the Invention
Liquid crystalline materials, because they can be manipulated between light scattering and light transmissive modes in response to applied electric fields, find use in a variety of display devices. These materials, which may have either positive or negative dielectric anisotropy, are generally classified as nematic or smectic. A particular type of nematic liquid crystals, referred to as chiral nematic, has the ability to selectively reflect one component of circularly polarized light. In the chiral nematic phase, which is synonymous with the cholesteric phase, chiral molecules form very thin layers of aligned molecules, the alignment in one layer being at a slight angle from that in an adjacent layer, and the alignment in a stack of such layers forming a continuous helical pattern.
Many known liquid crystal display devices make use of liquid crystalline materials dispersed in polymeric matrices. For example, U.S. Pat. No. 4,435,047, the disclosure of which is incorporated herein by reference, describes a liquid crystalline material, preferably nematic, of positive dielectric anisotropy dispersed in a polymeric encapsulating medium such as polyvinyl alcohol. Also, U.S. Pat. No. 4,685,771, the disclosure of which is incorporated herein by reference, describes a light-modulating liquid crystal display material that contains liquid crystalline microdroplets dispersed in a thermoplastic resin, the microdroplets being of a size effective to scatter incident light when the optical axes of the microdroplets are randomly aligned. U.S. Pat. No. 5,116,528, the disclosure of which is incorporated herein by reference, describes a light modulating material that includes a liquid crystalline material dispersed in a cross-linked isocyanate material, preferably a polyacrylic urethane. Also, U.S. Pat. No. 5,583,670, the disclosure of which is incorporated herein by reference, describes an information recording layer in which a liquid crystal phase is dispersed in an acrylic or methacrylic resin having a molecular weight of 25,000 to 100,000.
PCT/WTO 97/04398, entitled ELECTRONIC BOOK WITH MULTIPLE DISPLAY IMAGES, discloses the assembly of multiple electronically written display sheets into a xe2x80x9cbook.xe2x80x9d The reference describes prior art techniques for forming thin, electronically written pages, including flexible sheets, image modulating material formed from a bi-stable liquid crystal system, thin metallic conductor lines on each page, and transparent conducting polymers formed over the light modulating material.
Co-pending, commonly assigned U.S. application Ser. No. 09/379,776, filed Aug. 24, 1999 for FORMING A DISPLAY HAVING CONDUCTIVE IMAGE AREAS OVER A LIGHT MODULATING LAYER, the disclosure of which is incorporated herein by reference, describes a method for forming a display on a transparent substrate on which is formed a transparent, electrically conductive coating. A light modulating layer including liquid crystalline material in a polymer binder is formed over the electrically conductive layer, and an opaque conductive material is deposited in an imagewise pattern over the light modulating layer in the form of viewable and conductive images. The light modulating layer is effective in a first condition to prevent the viewing of the viewable and conductive images and in a second condition to permit the viewing of the viewable and conductive images. Electrical connections enable an electrical field to be applied across selected ones of the viewable and conductive images and the transparent electrically conductive layer to cause the light modulating layer underlying the selected images to change from the first condition to the second condition and thereby present the images for viewing by a viewer.
In the fabrication of a liquid crystal display as just described, a transparent, electrically conductive layer is formed on the substrate, followed by the formation of the light modulating layer comprising liquid crystalline material in a polymeric binder on the conductive layer.
The present invention is directed to a process for selectively removing a light modulating layer containing a liquid crystalline material dispersed in a polymeric binder from the electrically conductive layer of a liquid crystal display web. The provided web includes a flexible substrate, an electrically conducting layer disposed on the substrate, and a light modulating layer disposed on the electrically conductive layer. The light modulating layer comprises a liquid crystalline material dispersed in a polymeric binder and has an upper surface.
In accordance with the invention, the web is transported at a controlled rate of speed from a first station to a second station that is situated at a selected distance from the first station. At the first station, a solvent effective for softening the light modulating layer is applied at a controlled rate to a selected portion of the upper surface, thereby forming a selected softened portion of the light modulating layer. At the second station, the selected softened portion of the light modulating layer is selectively removed from the electrically conductive layer on the substrate.
In making liquid crystal displays, it is frequently necessary to make electrical connections to the underlying conductive layer, a task that is facilitated by the process of the present invention.